And a Rhinocerotoid Perissodactyl from the Middle Eocene Santiago Formation of Southern California

Home , Duchesnean, Epihippus, Hyracodon, Tapocyon, Uintan

Paludicola 11(1):8-30 October 2016 © by the Rochester Institute of Vertebrate Paleontology

NEW RECORDS OF EPIHIPPUS (EQUIDAE) AND A RHINOCEROTOID PERISSODACTYL FROM THE MIDDLE EOCENE SANTIAGO FORMATION OF SOUTHERN CALIFORNIA

Thomas S. Kelly1 and Paul C. Murphey2

1Research Associate, Vertebrate Paleontology Department, Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, California 90007 2Research Associate, Department of Paleontology, San Diego Museum of Natural History, 1788 El Prado, San Diego, California 92101

ABSTRACT Records of the middle Eocene equid Epihippus from the West Coast of North America are extremely rare. Previously, only one specimen was reported from California in a faunal list of the Mission del Oro Local Fauna from the Santiago Formation of San Diego County, but this specimen was never described or illustrated and its specific status remained undetermined. Subsequently, additional specimens of Epihippus from southern California have been discovered as the result of paleontological mitigation programs conducted for commercial development projects. Here we provide detailed accounts of all of the Epihippus specimens currently known from California, wherein we recognize the occurrence of two species, E. gracilis and E. uintensis. A rhinocerotoid, which likely represents either Uintaceras or Teletaceras, is also recorded from the Santiago Formation of San Diego County. In addition, a new middle Eocene fauna is documented, the Rancho Mission Viejo Local Fauna, which is the first fauna of the early Uintan North American Land Mammal Age recorded from Orange County.

INTRODUCTION Occurrences of middle Eocene horses are extremely rare in southern California. Walsh (1996b) Contrary to the early and late Eocene faunas of reported the first record of Epihippus in a faunal list North America, horses are a relatively rare of the Mission del Oro Local Fauna from the component in middle Eocene faunas of the Santiago Formation of San Diego County, but did not Bridgerian, Uintan and Duchesnean North American provide a description or illustration of the specimen. Land Mammal Ages, primarily being known from the Extensive, ongoing paleontological mitigation western interior and Gulf Coast Plain (Granger, 1908; programs have been conducted since 1996 in Matthew, 1929; McGrew, 1953; Gazin, 1976; southern California, which have resulted in new MacFadden, 1980,1998; Rasmussen, et al., 1999a, records of Epihippus from three additional localities 1999b; Froehlich, 2002; Kelly et al., 2012). During in the Santiago Formation (Figure 1). A the early Eocene Wasatchian North American Land rhinocerotoid specimen, which was not described or Mammal Age, horses were common and diverse, illustrated, was previously recorded from the including at least six genera and 13 species Santiago Formation of San Diego County and (Froehlich, 2002). By the beginning of the misidentified as Hyracodon sp. (Tomiya, 2012). Bridgerian, horse diversity had rapidly declined with These perissodactyl records are highly significant to only one genus, Orohippus Marsh, 1872, being our understanding of the middle Eocene recognized (MacFadden, 1998). Orohippus gave rise biostratigraphy of southern California. The purpose to Epihippus in the earliest Uintan and the latter gave of this report is to provide detailed accounts of all of rise to Duchesnehippus Peterson, 1931, in the the known specimens of Epihippus from California Duchesnean. During the late Duchesnean and reevaluate the taxonomic status of the Duchesnehippus gave rise to Mesohippus Marsh, rhinocerotoid specimen. 1875, which became abundantly represented by numerous species during the early Chadronian (late METHODS Eocene) through earliest Arikareean (early late Oligocene) North American Land Mammal Ages Measurements of teeth were made with an (MacFadden, 1998). optical micrometer to the nearest 0.01 mm. Equid dental terminology follows Froehlich (2002) and that 8

KELLY AND MURPHEY—EPIHIPPUS FROM SOUTHERN CALIFORNIA 9

time scale); N, number of specimens; R, right; SD, standard deviation; tr, greatest transverse width; tra, anterior transverse width; trp, posterior transverse width. Abbreviations for institutions and specimens cited in text are: OCPC, Orange County Paleontological Collection at the Dr. John D. Cooper Archaeological and Paleontological Center, Orange County, California; SDNHM, San Diego Natural History Museum; SDSNH, San Diego Society of Natural History.

GEOLOGIC SETTING

The type Santiago Formation was first named by Woodring and Popenoe (1945) for outcrops on Santiago Creek to the east of Irvine Park in the Santa Ana Mountains of Orange County, California. The Santiago Formation unconformably overlies the Paleocene Silverado Formation and unconformably underlies the middle Eocene (late Uintan) to Miocene Sespe Formation and/or the informal unit referred to by Whistler and Lander (2003) as the Sespe- Vaqueros Formations undifferentiated (see also Woodring and Popenoe, 1945; Morton, 1974; Schoellhamer et al., 1981; Prothero, 2001). In the type area, the formation is divided into two informal units, the lower and upper beds (Schoelhammer et al., 1981). The lower beds are characterized by medium FIGURE 1. Map of southern California coastal area showing to coarse grained, cross-bedded sandstones, greenish- geographic locations of middle Eocene localities that yielded Epihippus. 1, Rancho Mission Viejo (locality OCPC 03976), gray to reddish mudstones and conglomerate lenses Orange County. 2, Mission del Oro (locality SDSNH 3574), San near the base, whereas the upper beds are Diego County. 3, Ocean Ranch (locality SDSNH 4730), San characterized by medium to fine grained, poorly Diego County. 4, Legoland (locality SDSNH 4131), San Diego bedded sandstones, greenish-gray to reddish County. Insert map shows area covered by map. ______variegated sandy siltstones and claystones (Woodring and Popenoe, 1945; Morton, 1974). for Rhinocerotoidea follows Dashzeveg and Hooker In northern San Diego County, outcrops have (1997) except that we prefer the term cristid obliqua also been referred to the Santiago Formation by instead of metalophid for the cristid that extends Wilson (1972), wherein he recognized three informal anterolingually from the hypoconid to protolophid. members (members A, B and C). Based upon early Upper and lower teeth are designated by uppercase Uintan mammal faunas from the upper part of and lowercase letters, respectively. Open member B and correlation with Calcareous nomenclature qualifiers follow Bengtson (1988). All Nannoplankton Zones, Planktonic Foraminiferal specimens described here are curated in the research Zones, Benthic Foraminiferal Stages and West Coast collections at the Department of Paleontology at the Molluscan "Stages," Walsh (1996b) regarded San Diego Museum of Natural History, San Diego, member B of the Santiago Formation in northwestern California and the Orange County Paleontological San Diego County to span the late Bridgerian to early Collection at the Dr. John D. Cooper Archaeological Uintan North American Land Mammal Ages, or and Paleontological Center, Orange County, about 48-45.5 Ma, and a correlative to the La Jolla California. Detailed locality data are available at Group of southwestern San Diego County. Member these institutions. C of the Santiago Formation is separated from Subzones or biochrons of the Bridgerian and member B by an unconformity in northwestern San Uintan North American Land Mammal Ages (e.g., Diego County and has yielded middle Eocene Br3, Ui1a, Ui1b, Ui2, and Ui3) follow Gunnell et al. mammal faunas of late Uintan and early Duchesnean (2009). Ages (Walsh, 1996b; Walsh et al., 1996; Prothero, Abbreviations are: ap, greatest anteroposterior 2001; Mihlbachler and Deméré, 2009). Based on length; CV, coefficient of variation; L, left; Ma, magnetostratigraphy, Walsh et al. (1996) correlated megannum (one million years in the radioisotopic the La Jolla Group to Chron C21n and the lower third 10 PALUDICOLA, VOL. 11, NO. 1, 2016

of Chron C20r of the Global Polarity Time Scale, or SDSNH 43478, we reexamined it and provide a about 47.9-45.5 Ma. Prothero (2001) reported that detailed description below, which indicates that it the lower part of the type Santiago Formation in cannot be assigned to either Triplopus or Hyracodon. Orange County was entirely within a paleomagnetic ______normal zone, which he correlated to Chron C21n. Prothero (2001) was unable to sample the magnetostratigraphy of the upper part of the type Santiago Formation, so its polarity has not been determined. The Bridgerian-Uintan transition is regarded by most recent investigators as occurring within Chron C21n at about 47 Ma (e.g., Walsh, et al., 1996; Robinson et al., 2004; Gunnell, et al., 2009; Kelly and Murphey, 2016).

LOCALITIES AND FAUNAS

Mission del Oro—Walsh (1996b) named the Mission del Oro Local Fauna based on a fauna from three localities (SDSNH 3570, 3572, 3574) in member C of the Santiago Formation that were discovered during the grading of the Mission del Oro housing project, Oceanside, California (Figure 2, Table 1). The localities occur in brownish, gritty mudstones interbedded within coarse-grained, arkosic channel sandstones, about 9 to 10 m above the disconformity that separates members B and C. Locality SDSNH 3574 yielded the first record of Epihippus from California. Based primarily on the presence of Protylopus sp., cf. P. robustus Golz, 1976, in the fauna, Walsh (1996b) regarded the Mission del Oro Local Fauna to be a correlative of the Laguna Riviera Local Fauna from member C at the Laguna Riviera housing district, Carlsbad, and latest Uintan or earliest Duchesnean in age. Protylopus robustus is also known from the late Uintan Brea Canyon Local Fauna of the Sespe Formation of Ventura County, California (Kelly, 1990; Kelly et al., 1991; Kelly and Whistler, 1994).

Walsh (1996b) also noted that another locality (SDSNH 3235) at Mission del Oro, which occurs in FIGURE 2. Generalized stratigraphic column of Santiago an exposure that is separated from the section that Formation at Mission del Oro housing project showing localities yielded the Mission del Oro Local Fauna by a that yielded the Mission del Oro Local Fauna. Stratigraphic column modified after Walsh (1996b). covered portion and estimated to be about 30 to 35 m ______stratigraphically higher, yielded Duchesneodus uintensis and Amynodontopsis bodei, species which Rancho Mission Viejo—A small are generally regarded as characteristic taxa of the paleontological mitigation program was conducted in early Duchesnean (Rasmussen et al., 1999b; 2010 at Rancho Mission Viejo during the excavation Robinson et al., 2004; Kelly et al., 2012). Based and grading for a substation, which resulted in the upon a partial left dentary with m1-3 (SDSNH discovery a single locality (SDSNH 6407) that 43478), Tomiya (2012) listed the occurrence of yielded a small sample of fossil mammals. Hyracodon sp. from locality SDSNH 3574, a genus Subsequently, Kelly (2015) reported on the fossil that is generally considered as having its first mammals recovered from two additional localities appearance in the late Duchesnean (Krishtalka et al., (OCPC 03976 and OCPC 03988) at Rancho Mission 1987; Prothero, 1998; Kelly et al., 2012). However, Viejo that were discovered during an ongoing this specimen was originally cataloged as Triplopus, paleontological mitigation program for Rancho and Tomiya (2012) did not describe or illustrate the Mission Viejo Planning Area 2, conducted by specimen. In order to clarify the systematic status of Archaeological Resource Management Corporation KELLY AND MURPHEY—EPIHIPPUS FROM SOUTHERN CALIFORNIA 11

of Rancho Palos Verdes, California (Figure 3). TABLE 1. Faunal list of Mission del Oro Local Fauna from Planning Area 2 included the major excavation and localities SDSNH 3570, 3572, and 3574, Oceanside, San Diego County, California, member C, Santiago Formation, latest Uintan grading of a large area of the foothills along the north or earliest Duchesnean (Walsh,1996b; Tomiya, 2012; this paper). side of San Juan Creek, adjacent to the substation and between the mouths of Cañada Chiquita and Cañada Mammalia Gobernadora, Orange County, California. The Didelphomorphia Peradectidae paleontologic program at Rancho Mission Viejo has Peradectes californicus Stock, 1936 also resulted in the recovery of plant fossils, Lipotyphla including leaf and seed impressions, silicified logs Sespedectidae and palynomorph assemblages. In a mitigation report Sespedectes singularis Stock, 1935a Proterixoides davisi Stock, 1935a for the program, Fisk et al. (2015) documented a Rodentia plant assemblage from Rancho Mission Viejo Ischyromyidae consisting of ferns, cedars, alders, palms, magnolias, Microparamys sp. wild avocados, evergreen oaks and cattails, which Mytonomys sp Eohaplomys sp., cf. E. serus Stock, 1935b they interpreted to represent a lowland to montane Cylindrodontidae rain-forest community that was significantly wetter Pareumys sp. and warmer than the present day climate. Eomyidae The section exposed during excavation at the Metanoiamys sp. Geomyidae? Rancho Mission Viejo substation included about 6.6 Griphomys sp. m of Santiago Formation and about 3.2 m of Simimyidae unconformably overlying Quaternary terrace Simimys simplex (Wilson, 1935) deposits. The stratigraphy of the Santiago Formation Perissodactyla Rhinocerotoidea at the substation consisted of the following, in genus and species undetermined (probably ascending order: 1) a basal 0.61 m yellowish-grey Uintaceras or Teletaceras sp., not Hyracodon sandy siltstone containing locality SDSNH 6407; 2) sp. vide Tomiya [2012]) about 5 m of light gray, coarse grained sandstone; Brontotheriidae cf. Duchesneodus sp. and 3) about 1 m of yellowish-green siltstone. Equidae The two new vertebrate localities discovered Epihippus uintensis (Marsh, 1875) during excavation activities in 2013 and 2014, along Artiodactyla with SDSNH 6407, occur on the east side of Planning Agriochoeridae Protoreodon sp. Area 2. The lithology on the east side of Planning Oromerycidae Area 2 differs from that of the west side, which Protylopus sp., cf. P. robustus Golz, 1976 yielded most of the plant fossils. The west and east ______sides cannot be directly correlated because of local faulting, inconsistent small scour-filled channel cuts, which were articulated. Some taxa are represented the lack of marker beds that can be traced from one by either a single specimen or a few specimens, so side to the other, and the fact that a major fissure confident taxonomic allocation at the species level zone separates them. However in both sides of could not always be made with confidence. Planning Area 2, a series of fining up cycles (12 on Furthermore, generic level identifications were also the east side and 15 on the west side), each consisting difficult for some taxa due to the lack of intact of a sandstone unit and overlying claystone unit, were dentitions. Considering these facts, most generic recognized by Patrick Riseley (per. communication, referrals presented here are conservative (Table 2), 2015). Patrick kindly provided us with his wherein they are often only compared to (cf.) a stratigraphic sections of the east and west sides of genus, indicating that they either actually represent Planning Area 2, of which that of the east side the genus or a closely related genus (after Bengtson, containing the vertebrate fossil localities is shown in 1988). Nevertheless, the mitigation programs have Figure 4. resulted in the recognition of a relatively diverse Except for locality OCPC 03988, most of the mammalian fauna containing at least 18 taxa fossil mammals from Rancho Mission Viejo were representing seven orders from the Santiago recovered from bulk samples of screen-washed Formation at Rancho Mission Viejo (Table 2). This matrix, yielding small fossil containing concretions fauna is referred to the Rancho Mission Viejo Local that were then dissolved using peroxide. The Fauna. The presence of Palaeictops, Patriolestes concretions often contained a mixture of iron oxide davisi, Achaenodon robustus, Leptoreodon marshi, and green waxy claystone, which made preparation Protoreodon sp., cf. P. parvus, Merycobunodon and difficult. Many of the mammalian fossils recovered possibly Hesperolemur, taxa that have been were fragmentary, consisting of isolated teeth, partial previously recorded from the early Uintan Poway isolated teeth and appendicular elements, some of Fauna of the Friars Formation of southwestern San 12 PALUDICOLA, VOL. 11, NO. 1, 2016

FIGURE 3. Map showing the geographic locations of the three fossil localities (SDSNH 6407, OCPC 03976, and OCPC 03988) that yielded the Rancho Mission Viejo Local Fauna of Orange County, California. Details of section A-B shown in Figure 4. ______

Diego County and/or from the early Uintan portion of exposed on the east side of Rancho Mission Viejo are member B of the Santiago Formation of northwestern more probably non-marine because of the following: San Diego County (Walsh, 1996b), indicate a similar 1) the stratigraphy consists of sequences of channel age for the Rancho Mission Viejo Local Fauna. The sandstones, some with rip up clasts, and interbedded fauna is highly significant because it includes the siltstones and claystones that form a series of weakly largest sample of Epihippus from southern California fining up units that appear to represent multiple flood and is the first early Uintan North American Land events; and 2) only land mammals have been Mammal Age assemblage (biochron Ui1b) from the recovered (marine vertebrates and invertebrates are Santiago Formation of Orange County. lacking). Furthermore, Schoellhamer et al. (1981) Morton (1974) provided a geologic map of the regarded the upper part of the Santiago Formation in Gobernadora 7.5 minute Quadrangle, which included the type area along the north side of Santiago Creek Planning Area 2 at Rancho Mission Viejo. He as non-marine because silicified wood is commonly mapped the Santiago Formation in Planning Area 2 present, which is also true for the exposures at as the lower beds of the formation (= lower part of Rancho Mission Viejo. In addition, the upper part of Schoellhamer et al., 1981) and regarded them as member B of the Santiago Formation in San Diego marine because one locality in the Santiago County, which is regarded as a correlative of the Formation, which occurs outside and south of the upper part of the formation in Orange County mapped area, yielded the oyster, Ostrea stewartii. (Wilson, 1972), contains early Uintan mammals However, some portions of the Santiago Formation (Walsh, 1996b), which is also true for the section at KELLY AND MURPHEY—EPIHIPPUS FROM SOUTHERN CALIFORNIA 13

TABLE 2. Faunal list for Ranch Mission Viejo Local Fauna from TABLE 3. Faunal list for localities SDSNH 4730 (= localities OCPC 03976, OCPC 03988, and SDSNH 6407, Rancho Harpagolestes Quarry) and 5721, which are laterally equivalent, Mission Viejo substation and Planning Area 2 (subareas 2.1 and but 73 m apart on lot 18 of Phase 1B of the Ocean Ranch 2.2), Orange County, California, Santiago Formation, early Uintan Commercial Development Project, San Diego County, California, (Ui1b). member C, Santiago Formation, early Duchesnean (Deméré and Murphey, 2005; Mihlbachler and Deméré, 2009; Tomiya, 2012; Reptilia this paper). Squamata Anguidae, genus undetermined. Reptilia Mammalia Testudines Leptictida Trionychidae Leptictidae Trionyx sp. Palaeictops sp. Mammalia Lipotyphyla Didelphomorphia Geolabididae Herpetotheriidae Centetodon sp. Herpetotherium sp. Erinaceomorpha Peradectidae Sespedectidae Peradectes sp. Patriolestes davisi Walsh, 1998 Pantolesta Primates Pantolestidae Notharctidae Simidectes sp. cf. Hesperolemur sp. Lipotyphla Sespedectidae Canivoramorpha (sensu Bryant, 1996) Sespedectes sp. Viverravidae Proterixoides sp. cf. Viverravus sp. Oligoryctidae Carnivoriformes (sensu Flynn, Finarelli and Oligoryctes sp. Spaulding, 2010) Primates Miacidae Omomyidae Miacis spp. Dyseolemur sp. cf. Procyondictis sp. Ourayia sp. Rodentia Carnivoramorpha (sensu Bryant, 1996) Ischyromyidae Carnivoraformes (sensu Flynn, Finarelli and cf. Thisbemys sp. Spaulding, 2010) cf. Pseudotomus sp. A Lycophocyon hutchinsoni Tomiya, 2011 cf. Pseudotomus sp. B Tapocyon sp. Microparamys sp. Plesiomiacis sp. Eomyidae Miocyon sp. Metanoiamys sp. "Condylartha" Perissodactyla Mesonychidae Brontotheriidae Harpagolestes sp. brontothere, genus undetermined Rodentia Equidae Ischyromyidae Epihippus gracilis (Marsh, 1871) Microparamys sp. Artiodactyla Eohaplomys sp., cf. E. serus Stock, 1935b Helohyidae Cylindrodontidae Achaenodon robustus Osborn, 1883 Pareumys sp. Oromerycidae Eomyidae Merycobunodon sp. Metanoiamys marinus Chiment and Korth, Protoceratidae 1996 Leptoreodon marshi Wortman, 1898 Simimyidae Agriochoeridae Simimys simplex (Wilson, 1935) Protoreodon sp. cf. P. parvus Scott and Geomyidae? Osborn, 1887 Griphomys sp. artiodactyl, family undetermined Amynodontidae ______amynodont, genus undetermined Brontotheriidae Rancho Mission Viejo. In a mitigation report, Rugh cf. Parvicornus occidentalis Mihlbachler and Deméré, 2009 (2016) identified fossil invertebrates from another Equidae locality in the Santiago Formation at Rancho Mission Epihippus uintensis (Marsh, 1875) Viejo, including the following: 1) a few tropical land Artiodactyla snails; 2) a few species of gastropods and bivalves Dichobunidae Tapochoerus sp. characteristic of marine estuary mudflats; 3) two Agriochoeridae species of snails characteristic of freshwater lakes or Protoreodon walshi Theodor, 1999 ponds; and 4) one species of brackish water snail. Oromerycidae The freshwater snails were the most common Protylopus sp. Protoceratidae invertebrates at this locality. Rugh (2016) suggested Leptoreodon sp. that the invertebrate fossils may have been 14 PALUDICOLA, VOL. 11, NO. 1, 2016

to repeated flooding into a near shore estuarine embayment or intertidal mudflat. Contrary to Morton (1974), the presence of early Uintan land mammals indicates that the exposures of Santiago Formation at Rancho Mission Viejo most likely represent some portion of the upper part of the formation rather than the lower part. ______

TABLE 4 . Faunal list for SDSNH 4131, site 6 at Legoland project, Carlsbad, San Diego County, California, member C, Santiago Formation.

Mammalia Lipotyphla Sespedectidae cf. Proterixoides sp. Primates Omomyidae omomyid, genus undetermined Rodentia Ischyromyidae cf. Microparamys sp. Cylindrodontidae Pareumys sp. Eomyidae Metanoiamys sp. Geomyidae? Griphomys sp. Simimyidae Simimys sp. Perissodactyla Hyracodontidae Triplopus sp. Equidae Epihippus uintensis (Marsh, 1875) Artiodactyla Agriochoeridae Protoreodon sp. ______

Ocean Ranch—In a report for a paleontological mitigation program conducted at the Ocean Ranch FIGURE 4. Generalized stratigraphic column of section on east Commercial Development Project at Oceanside, San side of Planning Area 2 (see section A-B, Figure 3) at Rancho Mission Viejo showing relative stratigraphic positions of Diego County, California, Deméré and Murphey vertebrate fossil localities that yielded the Rancho Mission Viejo (2005) documented the discovery of numerous Local Fauna (modified section courtesy of Patrick Riseley, per. superposed localities in the Santiago Formation that communication, 2015). Abbreviations are: C, claystone; Fm., yielded fossils that span the early Uintan through the Formation; NALMA, North American Land Mammal Age; S, sandstone. early Duchesnean North American Land Mammal ______Ages. The section at Ocean Ranch consists of about 76 m of the Santiago Formation, including members transported a short distance from land and/or B and C, and unconformably overlying Quaternary freshwater lakes or ponds by monsoonal rains or stream terrace deposits. A detailed stratigraphic connecting channels to their final deposition along an framework was provided by Mihlbachler and Deméré estuary shoreline or mudflat. Thus, another possible (2009, figure 2) for the localities at Ocean Ranch and scenario that cannot be ruled out to explain the is summarized as follows, in ascending order: 1) occurrence of land mammals, terrestrial plants, about 21 m of member B of the Santiago Formation, silicified tree logs at the other Rancho Mission Viejo which yielded mammal fossils of early Uintan Age localities along with the lack of deep water marine and marine invertebrates (see also Schweitzer and invertebrates or marine vertebrates in the section, is Feldman, 2002); 2) 12 m of member C that is that the fossils were, at least in part, deposited in a separated from member B by an unconformity and non-marine environment that may have been subject characterized by a maroon sandstone unit that yielded mammals of late Uintan Age; 3) about 40 m of KELLY AND MURPHEY—EPIHIPPUS FROM SOUTHERN CALIFORNIA 15

Parvicornis occidentalis, from the Bones Sands localities and referred an associated partial skull and skeleton to cf. P. occidentalis from the Harpagolestes Quarry. Subsequently, Tomiya (2011) described a new basal carnivoramorphan, Lycophocyon hutchisoni, from member C of the Santiago Formation of San Diego County, which included specimens from the Bone Sands at Ocean Ranch. Although Mihlbachler and Deméré (2009) reported that Epihippus occurred in the Bone Sands, only a single specimen of Epihippus was recovered at Ocean Ranch, which actually came from locality SDSNH 4730. Also, it should be noted that Mihlbachler and Deméré (2009) mistakenly listed locality SDSNH 5721 as the Harpagolestes Quarry, but in fact the quarry occurred at locality SDSNH 4730, which is laterally equivalent to SDSNH 5721. A faunal list for localities SDSNH 4730 and 5721 is provided in Table 3. Legoland—Locality SDSNH 4131 was discovered in 1997 during grading for the development of the theme park Legoland in Carlsbad, California. The locality occurred approximately 244 m West of Hidden Valley Road in Legoland at an elevation of about 23 m and is now a landscape covered area within the park. The fossils were recovered by quarrying the fossiliferous horizon along with wet screen washing of 400 lbs of bulk matrix from the site. The exposed section at locality SDSNH 4131 was identified as member C of the Santiago Formation and is composed of the following units, in ascending stratigraphic order (Figure 5): 1) 15 to 17 m of light to dark brown siltstones; 2) a 1.6 m unit consisting of a basal white sandstone with siltstone rip up clasts containing locality SDSNH 4131 and an

FIGURE 5. Generalized stratigraphic column of exposed section overlying 0.17 m thick dark brown mudstone; 3) a containing locality SDSNH 4131 at site 6, Legoland. second 1.6 m fining up unit, which has an erosional ______disconformity at its top of up to 0.9 m, consisting of a basal white sandstone and overlying dark brown interbedded siltstones and sandstones, which are siltstone; and 4) 3.6 m of course, cross-bedded separated from the maroon sandstone unit by a sandstone. The mammals recovered from locality disconformity, that yielded early Duchesnean SDSNH 4131 include taxa that are known from both mammals from two localities (SDSNH 4730 = the late Uintan and early Duchesnean, so the fauna Harpagolestes Quarry, and SDSNH 5721) within a could be either age (Table 4). 0.3 m thick siltstone layer and overlying 0.6 - 1 m muddy sandstone bed near the middle of the unit that SYSTEMATIC PALEONTOLOGY represent an undulating channel deposit; 4) 10 to 15 m of channel filled sandstone sequences, referred to Class Mammalia Linnaeus, 1758 as the Bone Sands, which yielded mammals of early Order Perissodactyla Owen, 1848 Duchesnean age; and 4) about 16 to 17 m of stream Family Equidae Gray, 1821 terrace deposits, which unconformably overlie the Genus Epihippus Marsh, 1878 Santiago Formation, that yielded mammal fossils of Epihippus gracilis (Marsh, 1871) Pleistocene age. Although most of the fossil Figures 6A-H, Table 7 mammals from Ocean Ranch have not been formally described, Mihlbachler and Deméré (2009) Referred Specimens―From locality OCPC documented a new genus and species of brontothere, 03976 (Mission Rancho Viejo): RM1 or 2, OCPC 16 PALUDICOLA, VOL. 11, NO. 1, 2016

76439, 80084; LM1 or 2, OCPC 76440, 80097; the protolophid, just below and posterolabially of the partial right upper cheek teeth, OCPC 80087, 85391; metaconid apex. The posthypocristid is short, partial Rp4?, OCPC 73188; partial lower right cheek extending posterolabially from the hypoconid to a tooth, OCPC 73198. small hypoconulid. A moderately strong, continuous Description―The four complete upper molars cingulid composed of the anterior, labial and exhibit posterior appression facets, eliminating the posterior cingulids is present, which extends around possibility that any of them represent M3. Based on the tooth from the anterolabial base of the protoconid their occlusal outlines and relative sizes, they most to the posterolabial base of the entoconid. likely represent M1 or 2. The tooth positions for the ______partial upper and lower cheek teeth are less certain, but, based on relative size, OCPC 73198 probably TABLE 5. Combined dental measurements (in mm) and statistics represents m1 or 2 and OCPC 73188 probably of middle Eocene specimens of Epihippus gracilis and Epihippus uintensis showing large observed ranges (OR) and high represents p4. coefficients of variation (CV>10) for most all dental The upper cheek teeth are relatively low- measurements, which, contrary to Hanson (1996), does not appear crowned with a quadrate occlusal outline. The to support a single species scenario. Measurements from Peterson parastyle is moderately robust. A distinct mesostyle (1931) Gazin (1956), Bjork (1967), Forstén (1971), MacFadden (1980), Westgate (1990), McCarrol et al. (1996) and this paper. is present between the paracone and metacone. The four primary cusps (paracone, metacone, protocone Position/ and hypocone) are distinct, with the paracone taller dimension N Mean OR SD CV and slightly larger than the metacone, and the P2 ap 5 6.86 6.0-8.4 0.971 14.2 protocone slightly larger and positioned slightly more tr 5 5.54 5.1-6.5 0.611 11.0 lingually than the hypocone. The protoloph is P3 ap 6 6.90 6.2-8.5 0.817 11.8 moderately tall, extending anterolabially from the tr 6 6.93 6.6-7.5 0.399 5.6 protocone to a distinct protoconule and then P4 ap 6 7.62 6.2-9.3 1.241 16.3 tr 6 8.92 7.6-10.4 1.070 12.0 continues to the anterolingual base of the paracone. M1 ap 6 8.50 7.0-9.6 0.938 11.0 The metaloph is moderately tall, extending tr 6 10.08 8.0-11.6 1.440 14.3 anterolabially from the hypocone to a moderately M2 ap 6 8.38 7.0-9.3 0.926 11.1 distinct metaconule and then continues to the tr 6 10.72 9.2-12.3 1.290 12.0 M3 ap 4 8.93 7.5-10.1 1.110 12.4 anterolingual base of the metacone. The anterior and tr 6 10.82 8.7-12.3 1.570 14.5 posterior cingula are robust. A distinct lingual p2 ap 9 7.16 5.3-8.4 0.967 13.5 cingulum is present between the protocone and tr 11 3.67 2.9-4.5 0.578 15.8 hypocone that commonly extends anteriorly across p3 ap 30 7.53 6.2-9.1 0.848 11.3 tr 26 4.82 3.6-6.0 0.667 13.8 the lingual base of the protocone to connect with the p4 ap 26 7.72 6.4-9.1 0.745 9.7 anterior cingulum (4 of 6 specimens), but only tr 25 5.47 4.3-6.5 0.702 12.8 extends posteriorly across the lingual base of the m1 ap 21 8.08 6.3-9.3 0.747 9.3 hypocone to connect with the posterior cingulum in tr 20 5.65 4.2-6.8 0.760 13.4 m2 ap 19 8.56 6.8-9.8 0.781 9.1 half of the specimens. tr 17 5.84 4.7-6.8 0.572 9.8 The two lower cheek teeth are broken. OCPC m3 ap 16 11.15 9.6-12.9 1.203 11.2 73188 is missing the labial portion of the protoconid tr 16 5.44 4.5-6.2 0.534 10.2 and the anterior wall of the tooth, including the ______paralophid, and OCPC 73198 is missing the Discussion―Unlike early Eocene equids, posterolabial corner of the hypoconid and much of Epihippus is a relatively rare component of middle the lingual edge of the tooth, including most of the Eocene faunas (Granger, 1908; Peterson, 1931; entoconid. Also, in OCPC 73198, the lingual portion Stirton, 1940; Gazin, 1956, 1976; Bjork, 1967; of the protolophid is displaced (folded) anteriorly. Forstén, 1971; MacFadden, 1980, 1998; Hanson, Even in their broken state, certain characters, which 1996; McCarroll et al., 1996). In the first major are typical of early equids, can still be discerned. revision of North American Eocene equids, Granger The teeth are moderately low-crowned, with length (1908) recognized two species of Epihippus from the greater than width. The paraconid and metaconid are Uintan; E. gracilis (Marsh, 1871) with E. uintensis transversely compressed, while the hypoconid and (Marsh, 1875) as its junior synonym, and a new metaconid are robust and conical. A distinct species, E. parvus. Peterson (1931) described paracristid (or paralophid) descends anteriorly from Duchesnehippus intermedius from the middle the protoconid apex and then turns lingually. The Duchesnean Lapoint Fauna of the Duchesne River protolophid is moderately tall, connecting the Formation of Utah. MacFadden (1980) reevaluated protoconid to the metaconid. A tall cristid obliqua the taxonomy of Epihippus and provided several extends anterolingually from the hypoconid, conclusions. He regarded the characters used by terminating relatively high on the posterior wall of Granger (1908) to distinguish E. parvus from E. KELLY AND MURPHEY—EPIHIPPUS FROM SOUTHERN CALIFORNIA 17

FIGURE 6 . Epihippus gracilis from Rancho Mission Viejo. A, LM1 or 2, OCPC 76440. B, RM1 or 2, OCPC 76439. C, RM1 or 2, OCPC 80084. D, LM1 or 2, OCPC 80097. E, partial right upper cheek tooth, OCPC 80087. F, partial right upper cheek tooth, OCPC 85391. G, partial Rp4?, OCPC 73188. H, partial right lower cheek tooth, OCPC 73198. All occlusal views. Bar scale = 5 mm.

18 PALUDICOLA, VOL. 11, NO. 1, 2016

TABLE 6. Measurements (in mm) of Epihippus gracilis, E. uintensis and Duchesnehippus intermedius (from Peterson, 1931; Gazin, 1956; Bjork, 1967; Forstén, 1971; MacFadden, 1980; Westgate, 1990; McCarrol et al., 1996; this paper). Contrary to Hanson (1996), we tentatively recognize E. uintensis as distinct from E. gracilis and consider the two specimens from the Hancock Quarry, Clarno Formation, Oregon, that he referred to E. gracilis as representing E. uintensis instead. N = number of specimens; OR = observed range; SD = standard deviation.

Position/ E. gracilis E. uintensis D. intermedius dimension N Mean OR SD N Mean OR SD N Mean OR P2 ap 4 6.48 6.0-7.1 0.519 1 8.4 - - - - - tr 4 5.30 5.1-5.8 0.337 1 6.5 - - - - - P3 ap 5 6.58 6.2-6.9 0.259 1 8.5 - - - - - tr 5 6.94 6.6-7.5 0.378 1 6.9 - - - - - P4 ap 3 6.63 6.2-7.5 0.751 3 8.60 8.1-9.3 0.624 1 8.8 - tr 3 8.03 7.6-8.6 0.513 3 9.80 9.4-10.4 0.529 1 10.6 - M1 ap 2 7.40 7.0-7.8 - 4 9.05 8.7-9.6 0.387 1 10.1 - tr 2 8.35 8.0-8.7 4 10.95 10.4-11.6 0.592 1 13.4 - M2 ap 3 7.60 7.0-8.0 0.529 3 9.17 9.0-9.3 0.153 1 11.2 - tr 2 9.40 9.2-9.6 - 3 11.60 11.2-12.3 0.608 1 12.9 - M3 ap 1 7.5 - 3 9.40 8.7-10.1 0.700 - - - tr 2 8.95 8.7-9.2 - 4 11.75 10.6-12.3 0.777 - - - p2 ap 5 6.66 5.3-7.7 0.888 4 7.76 7.1-8.4 0.723 1 9.0 - tr 6 3.23 2.9-3.8 0.327 5 4.20 3.9-4.5 0.255 1 4.5 - p3 ap 15 6.82 6.2-7.6 0.434 15 8.19 7.3-9.1 0.562 1 8.5 - tr 13 4.27 3.6-5.5 0.541 13 5.28 4.6-6.0 0.406 1 6.0 - p4 ap 14 7.02 6.4-7.7 0.464 12 8.37 7.5-9.1 0.485 2 8.85 8.7-9.0 tr 13 4.90 4.3-6.0 0.550 12 6.00 5.5-6.5 0.323 2 6.35 6.0-6.7 m1 ap 11 7.49 6.3-8.2 0.523 10 8.58 8.0-9.3 0.492 2 9.20 9.0-9.4 tr 10 4.99 4.2-5.8 0.537 10 6.04 5.4-6.8 0.461 2 6.35 6.0-6.7 m2 ap 7 7.78 6.8-8.7 0.698 12 8.70 7.6-9.8 0.644 2 9.25 9.0-9.5 tr 5 5.15 4.7-5.7 0.420 12 5.94 5.3-6.4 0.374 2 6.35 6.0-6.7 m3 ap 7 10.34 9.6-11.5 0.602 9 11.90 10.8-12.9 0.804 - - - tr 7 5.09 4.5-5.6 0.472 9 5.53 4.8-6.2 0.544 - - - ______

gracilis as unjustified and placed E. parvus in No large samples of Epihippus from a single synonymy with E. gracilis. Based primarily on size, quarry or stratigraphic horizon are available, so the he regarded E. uintensis as specifically distinct from amount of individual variation in dental size for E. gracilis, with the former being larger than the either E. gracilis or E. uintensis cannot be latter. MacFadden (1980) further considered that the confidently determined. If one accepts Hanson's characters used by Peterson (1931) to distinguish D. (1996) proposal that E. gracilis and E. uintensis are intermedius from E. uintensis did not rise to the level conspecific and the measurements of all the of generic or specific separation and placed D. specimens of both species previously reported in the intermedius in synonymy with E. uintensis. Hanson literature are combined with those documented here (1996) followed MacFadden (1980) and regarded (Table 5), then the resulting observed ranges for the Duchesnehippus as a junior synonym of Epihippus, dental dimensions are much larger and their but considered D. intermedius a valid species. respective coefficients of variation are much higher Hanson (1996) also regarded E. uintensis as a junior than one would expect for a single species (Simpson synonym of E. gracilis. Contrary to Hanson (1996), et al., 1960; Gingerich, 1974, 1979; Freudenthal and MacFadden (1998) continued to recognize E. Bescos, 1984; Carrasco, 1998). However, based on uintensis as specifically distinct from E. gracilis. size, the dental measurements of a number of small Rasmussen et al. (1999b, p. 424) resurrected samples from different middle Eocene localities do Duchesnehippus as generically distinct from appear to support separating E. gracilis from E. Epihippus, based on a partial lower molar from the uintensis even though there is some overlap in their Lapoint Member, Duchesne River Formation, that dental dimensions (Table 6). Thus, we follow agrees "in size, robustness and crown height with the MacFadden (1980, 1998) and tentatively recognize E. teeth of the holotype of D. intermedius" from the Dry uintensis as specifically distinct from E. gracilis. Gluch Creek Member, Duchesne River Formation. However, we recognize that if a single, large sample Kelly et al. (2012) also regarded Duchesnehippus as of Epihippus is discovered that exhibits the observed generically distinct from Epihippus based its greater range of dental measurements of both species, then molarization of the lower premolars (especially p2), synonymy would be justified with E. gracilis having greater hypsodonty and increased size. Robinson et priority. al. (2004) tentatively included the first appearance of The early Uintan sample of Epihippus from Duchesnehippus intermedius in their characterization Rancho Mission Viejo agrees well in size to E. of the beginning of the Duchesnean. gracilis and is referred to the species. KELLY AND MURPHEY—EPIHIPPUS FROM SOUTHERN CALIFORNIA 19

______is large, connected to the paracone and metacone by a strong centrocrista, which along with the TABLE 7. Measurements (in mm) of Epihippus gracilis preparacrista and postmetacrista, give the ectoloph a specimens from Rancho Mission Viejo (b = broken dimension; lct wide W-shaped occlusal pattern. The paraconule is = lower cheek tooth; p = partial; uct = upper cheek tooth). robust. The metaconule is distinct, but smaller and Specimen Position ap tra trp less cuspate than the paraconule. The anterior and OCPC 76439 RM1 or 2 8.19 9.75 9.05 posterior cingula are prominent, whereas the lingual OCPC 76440 LM1 or 2 7.36 8.60 7.95 cingulum is weak and does not extend across the OCPC 80097 LM1 or 2 8.50 9.50 8.30 OCPC 80084 RM1 or 2 7.95 9.83 8.70 lingual bases of the protocone or hypocone. OCPC 80087 p. R uct 7.60b - - The P4 is similar to the P3, but differs in being OCPC 85391 p. R uct 7.50b - 7.26b larger and more transverse, that is, relatively less OCPC 73188 p. Rp4? 5.65b - 5.58 expanded anteroposteriorly due to a relatively more OCPC 73198 p. R lct 7.04b 5.35b - ______closely positioned parastyle. The P4 also differs from the P3 by having a slightly more distinct protoconule Epihippus uintensis (Marsh, 1875) and metaconule and slightly stronger anterior and Figures 7A-G, 8A-C and 9A-D, Table 8 posterior cingula. Of the upper molars of SDSNH 105765, only Referred Specimens―From locality SDSNH the LM3 is complete. The M2s on both sides of 3574 (Mission del Oro): partial left dentary with SDSNH 105765 are damaged, missing most of their partial p2-3, complete p4-m1, partial m2 and labial portions, so little can be said of their occlusal associated partial upper cheek tooth, SDSNH 43476. morphology. The RM1 has a small portion of the From locality SDSNH 4730 (Ocean Ranch): parastyle broken away, but it is assumed that it had a associated partial fragmented skull with complete similarly developed one as those of the P4 and M3. RP1-M1, partial RM2-3, LP1, partial LP2-M2, The occlusal morphology of the RM1 of SDSNH complete LM3, partial dentaries with complete Rp2- 105765 is similar to those of the four M1 or 2s of E. m3 and complete Lp3-m3, isolated Li2 or 3, Lc, gracilis from Rancho Mission Viejo, but is larger in Lp1, and bone fragments, SDSNH 105765. From size. The M1 of SDSNH 105765 has a quadrate locality SDSNH 4131 (Legoland): Lm2, SDSNH occlusal outline with four large primary cusps 65006. (paracone, protocone, metacone, and hypocone). A Description―The skull is highly fragmented so robust mesostyle is present between the paracone and little can be said for its morphology, except that the metacone. The protoloph extends from the protocone infraorbital foramen occurs above the anterolabial to a distinct protoconule and then continues, root of P4. terminating just anterior of the anterior base of the To the best of our knowledge, the P1 of E. paracone. The metaloph extends from the hypocone uintensis has not been previously described. It has an to a weak metaconule and then continues, terminating oval occlusal outline, two distinct roots and a single, near the anterolingual base of the metacone. The tall central cusp. The anterior crest sharply declines anterior and posterior cingula are prominent, whereas from the central cusp to terminate at the anterolabial the lingual cingulum varies from being weak on M1, base of the tooth. The posterior crest first declines not extending anteriorly or posteriorly across the rapidly from the central cusp, but then slows its labial bases of the protocone and hypocone, declination as a more gentle slope resulting in it respectively, to moderately strong on M2, extending being longer than the anterior crest, and ends at the across their labial bases. The occlusal morphology of posterior base of the tooth. A very weak lingual the M3 is very similar to that of the M1 except for cingulum is present. being relatively narrower posteriorly. The M3 The P2 has a triangular occlusal outline and is lingual cingulum is also stronger than those of P3- submolariform with a distinct paracone, metacone M2. and protocone. The mesostyle is small, but distinct. The sample of lower teeth associated with the A very small parastyle is present at the anterior skull from Ocean Ranch include the i2 or 3, canine, terminus of the premetacrista. Anterior and posterior and p1-m3. The partial dentary from Mission del cingula are present, with the anterior cingulum joined Oro includes a partial p2-3, p4-m1 and partial m2, to and continuous with a distinct lingual cingulum whereas only an isolated lower molar (probably m2) that ends at the anterior base of the protoconid. was recovered from Legoland. Based on their similar The P3 has a quadrate occlusal outline and is sizes and the fact that no distinguishing dental fully molariform, with four robust primary cusps characters can be discerned among these specimens, (paracone, protocone, metacone and hypocone). The they are all regarded as conspecific. The two partial parastyle is relatively tall and cuspate. The mesostyle dentaries associated with the skull from Ocean Ranch are the most complete, but are distorted anteriorly. 20 PALUDICOLA, VOL. 11, NO. 1, 2016

FIGURE 7. Epihippus uintensis from Mission del Oro, Legoland and Ocean Ranch. A-C, antemolar teeth associated with SDSNH 105765: A, Li2 or 3; B, left canine; C, Lp1. D, Lm2, SDSNH 65006. E, partial right upper cheek tooth and F-G, associated partial left dentary with partial p2-3, p4-m1 and partial m2, SDSNH 43476. A-C and G, labial views. D-F, occlusal views. Bar scale = 5 mm.

KELLY AND MURPHEY—EPIHIPPUS FROM SOUTHERN CALIFORNIA 21

FIGURE 8 . Epihippus uintensis from Ocean Ranch. A-C, partial skull with LP1, partial LP2-M2, LM3, RP1-M1 and partial RM2-3, SDSNH 105765: A, close up occlusal views of RP1-M3; B, close up occlusal views of LP1-M3; C, ventral view of fragmented partial skull. Bar scales = 5 mm. ______

They are moderately robust with the depths below the small cuspid is present at the anterolabial corner of center of m1 being 17.6 and 17.7 mm. An associated the tooth that has a ridge or crest extending fragment preserving the anterior portion of the right posteriorly from it in a gentle arc to the posterolabial dentary of SDSNH 105765 has a c-p1 alveolar corner of the tooth, which then turns lingually and diastema length of 8.5 mm. continues, terminating at about the middle of the The lower incisor has a typical hyracothere labial base of the tooth. The central labial portion has morphology. The occlusal outline is triangular. A 22 PALUDICOLA, VOL. 11, NO. 1, 2016

FIGURE 9. Epihippus uintensis from Ocean Ranch. A-D, partial dentaries associated with partial skull, SDSNH 105765: A and D, partial left dentary with p2-m3; B and C, partial right dentary with p2-m3. A-B, occlusal views. C-D, labial views. Bar scales = 5 mm. KELLY AND MURPHEY—EPIHIPPUS FROM SOUTHERN CALIFORNIA 23

TABLE 8. Measurements (in mm) of Epihippus uintensis from southern California (a = approximate; b = broken dimension; p = partial; uct = upper cheek tooth).

Fauna (Locality) Specimen Position ap tra trp Mission del Oro L.F. (SDSNH Loc. 3574) SDSNH 43476 p. R uct 8.09b - 8.37 p. Lp2 - - 3.55 p. Lp3 7.21 - 5.45 Lp4 7.45 5.85 5.99 Lm1 8.70 6.46 6.54

Legoland (SDSNH Loc. 4131) SDSNH 65006 Lm2 9.83 5.85 6.23

Ocean Ranch (SDSNH Loc .4730, Harpagolestes Quarry) SDSNH 105765 LP1 4.40 2.74 - RP1 4.42 2.65 - p. LP2 7.37b - - RP2 7.40 4.30 5.81 RP3 8.34 8.31 7.85 RP4 8.70 - 9.0a RM1 8.89a 11.85a 10.85a LM3 9.50 11.02 9.35 Li2 or 3 3.09 1.70 - Lc 3.33 2.15 - Lp1 4.14 2.35 - Lp2 6.75 2.95 3.47 Rp2 6.72 2.93 3.46 Lp3 7.76 4.59 5.20 Rp3 7.75 4.57 5.37 Lp4 8.09 5.55 5.80 Rp4 8.02 5.66 5.96 Lm1 8.54 6.48 6.50 Rm1 8.45 6.32 6.35 Lm2 9.01 6.56 6.65 Rm2 9.30 6.50 6.76 Lm3 12.17 5.97 6.08 Rm3 12.20 6.08 5.95 Lp2-p4 22.2 - - Lm1-3 29.7 - - Rm1-3 29.9 - -

______

a concave, shallow, triangular basin and cingulids are with a weak posterior ridge that descends from the lacking. primary cuspid in a gentle arc, terminating at an The canine is simple in structure, with a single, incipient cuspid (slight bulge) at the posterior edge of robust root and a central primary cuspid. An anterior, the tooth. centrally positioned ridge extends anteriorly in a The p2 is submolariform, with the length gentle arc from the central cuspid to the base of the considerably longer than the width. A small, low crown and a posterior, centrally positioned ridge paraconid is positioned at the anterior margin of the descends rapidly from the central cuspid, terminating tooth. The protoconid is tall, with its apex slightly at the posterior base of the crown. The canine is expanded lingually, resulting in slight bulge that relatively small compared to the associated lower could be regarded as an incipient metaconid. The incisor and p1, suggesting that SDSNH 105765 hypoconid is large with a low cristid obliqua probably represents a female (following Gingerich, extending anterolingually from its apex to the base 1981). of the protoconid. The entoconid is small, but The p1 has a single, relatively tall primary distinct, whereas the hypoconulid is minute. Anterior, cuspid, which is positioned slightly anteriorly, and a posterior and labial cingulids are lacking. single, straight root that has a slight crease along the The p3 is fully molariform. The paracristid (= center of its labial surface. A weak, anterior ridge is paralophid) is low, descending rapidly from the present that descends rapidly from the primary protoconid to a very weak paraconid and then turns cuspid, terminating at the base of the crown, along lingually, terminating at the anterolingual corner of 24 PALUDICOLA, VOL. 11, NO. 1, 2016

the tooth. A robust, tall protoconid and slightly Referred Specimen―From locality SDSNH transversely expanded, tall metaconid are present, 3574: partial left dentary with partial m1, m2, and connected by a distinct protolophid. The hypoconid partial m3, SDSNH 43478. is robust, wide and slightly larger than the Description―SDSNH 43478 was cataloged as protoconid. A prominent entoconid is present that is a partial left dentary with p4-m2. However, a series connected to the hypoconid by a moderately strong of radiographs were taken of the dentary posterior to hypolophid. The hypoconulid is very small, the last tooth (Figure 10C), which demonstrated that positioned at about the center of the posterior no hidden unerupted tooth was present, indicating the cingulid and connected to the hypolophid by a short, last tooth is actually m3, so only m1-3 are present. low cristid (postcristid). The cristid obliqua is robust, The m2 is relatively complete, but the m1 is but low, extending anterolingually from the fragmented and missing the hypoconid and a portion hypoconid to the base of the protolophid, just of the metalophid, while the m3 has portions of the slightly lingual of its center. The anterior and entoconid and lingual hypolophid broken off. The posterior cingulids are relatively weak. A moderately lower molars have typical rhinocerotoid occlusal strong lingual cingulum is present that is continuous patterns with two primary transverse lophids with the posterior cingulid and crosses the labial base (protolophid and hypolophid) connecting the of the hypoconid, but does not continue anteriorly protoconid to the metaconid and the hypoconid to the across the labial base of the protoconid. entoconid, respectively. They are moderate in height The p4-m2 are very similar in occlusal (ratio of m3 protoconid height/m3 ap = 0.43). The morphology to that of the p3, but several differences paralophid descends anteriorly from the protoconid can be seen. The metaconid is more expanded apex to an indistinct paraconid (slight widening) and transversely with an incipient metastylid often then turns sharply lingually to end at a point just present on the anterolabial edge of the metaconid (an labial of the metaconid apex. The cristid obliqua (= incipiently twinned metaconid). The cristid obliqua metalophid of some authors; e.g., Radinsky, 1969; is slightly more robust and relatively taller in height. Hanson, 1989) descends rapidly from the hypoconid The labial cingulum is stronger and continuous across apex, terminating near the base of the protolophid, the labial bases of the protoconid and hypoconid, just lingual of the protoconid apex. On m2, the connecting anteriorly and posteriorly with the anterior and posterior cingulids are moderately anterior and posterior cingulids, respectively. strong, but do not extend beyond the anterolabial The occlusal morphology of the m3 is base of the protoconid or posterolabial base of the essentially identical to those of p4-m2 except that it hypoconid, respectively, whereas on m3, the anterior possesses a large, lobed, posteriorly projecting and posterior cingulids are slightly more robust and hypoconulid. join a very weak labial cingulum that extends across Discussion―The primitive equid, Haplohippus the labial bases of the protoconid and hypoconid. texanus McGrew, 1953, is known from the late ______Duchesnean Porvenir Local Fauna of Texas and the latest Uintan or earliest Duchesnean Clarno TABLE 9. Measurements (in mm) of Rhinocerotoidea, genus Formation of Oregon (Hanson, 1996). Although the undetermined (probably Uintaceras or Teletaceras) from Mission del Oro Local Fauna, locality SDSNH 3574 (a = approximate; b = p1 of SDSNH 105765 has a slight crease along the broken dimension; p. = partial). labial face of the root, which might be a remnant from the fusion of two roots, it can be easily Specimen Position ap tra trp distinguished from H. texanus by lacking the SDSNH 43478 p. Lm1 22.1b - 10.1b p. Lm2 27.20 16.42 17.33 primitive hyracothere state of two distinct roots on Lm3 27.30 17.53 17.80 p1, being smaller in size, and having a significantly Lm1-3 77a - - shorter c-p1 diastema and greater molarization of the ______p2-3. All of the above differences are diagnostic characters of Epihippus (McGrew, 1953; MacFadden, Discussion―SDSNH 43478 was originally cataloged 1976, 1980, 1998; Hanson, 1996). Based on size, the as a partial left dentary with p4-m2 of Triplopus. samples of Epihippus from Mission del Oro, Ocean Tomiya (2012) reidentified SDSNH 43478 as Ranch and Legoland are referred to E. uintensis. Hyracodon sp. without explanation. This assignment may have been due to the previous identification of Superfamily Rhinocerotoidea Owen, 1845 the teeth of SDSNH 43478 as being p4-m2, wherein family and genus undetermined the putative p4 would be regarded as fully Figures 10A-C , Table 9 molariform, similar to those of Hyracodon, and the fact that its molars are significantly larger than those of Triplopus. If this referral was correct, it would have been highly significant because the previous

KELLY AND MURPHEY—EPIHIPPUS FROM SOUTHERN CALIFORNIA 25

FIGURE 10. Rhinocerotoidea, genus and species undetermined (probably Uintaceras or Teletaceras sp.) from Mission del Oro. A-B, partial left dentary with partial m1, m2-3, SDSNH 43478. A, occlusal view. B, labial view. C, example of one of the radiographs taken of dentary posterior to last molar showing that no unerupted tooth is present. Bar scale = 10 mm. ______earliest record of Hyracodon is from the middle significantly larger. Although the familial status of Duchesnean Halfway/Lapoint Fauna of Utah Uintaceras has not been determined, it is generally (Radinsky, 1967; Prothero, 1998; Rasmussen et al., regarded as the closest sister taxon to the 1999b; Kelly et al., 2012). However, SDSNH 43478 Rhinocerotidae (Holbrook and Lucas, 1997; Prothero, can be easily distinguished from Hyracodon by the 2005). SDSNH 43478 is intermediate in size following: 1) relatively lower crowned; 2) a between Teletaceras radinskyi Hanson, 1989, and slightly weaker, relatively lower paralophid, not Uintaceras radinskyi Holbrook and Lucas, 1997, extending as far lingually; 3) a rapidly descending wherein its lower molar lengths are about 9% larger cristid obliqua, terminating near the posterior base of than the largest specimen of T. radkinskyi and about the protoconid; and 4) larger size. The lower molars 9-14% smaller than those of the smallest specimens of SDSNH 43478 are most similar in occlusal of U. radkinskyi. Unfortunately, besides size, morphology to those of the rhinocerotoid Uintaceras knowledge of the morphologies of the upper cheek and the primitive rhinocerotid Teletaceras (Hanson, teeth, lower premolars, incisors and manus are 1989; Holbrook and Lucas, 1997; Prothero, 2005). needed to distinguish Teletaceras from Uintaceras; They differ from those of Hyrachyus by being these characters are unknown for the Mission del Oro 26 PALUDICOLA, VOL. 11, NO. 1, 2016

form. It is likely that SDSNH 43478 represents Wyoming, Montana and Texas (MacFadden, 1980, either Uintaceras or Teletaceras and its intermediate 1998; Eaton, 1985; Gunnell et al., 2009). Storer size between U. radkinskyi and T. radinskyi suggests (1984) referred eight isolated teeth from the late that it may be a new species. Thus, contrary to Uintan Swift Current Creek Local Fauna of Tomiya (2012), SDSNH 43478 does not represent Saskatchewan to Epihippus sp., cf. E. gracilis. Hyracodon, so the currently accepted first appearance However, based on Storer's (1984) measurements of of the genus (Radinsky, 1967; Prothero, 1998; these teeth, they appear to represent E. uintenisis Rasmussen et al., 1999b; Kelly et al. 2012) remains instead. Hanson (1996) regarded E. uintensis as a unchanged. junior synonym of E. gracilis and referred two specimens from the Hancock Quarry of the Clarno CONCLUSIONS Formation of Oregon to Epihippus sp., cf. E. gracilis. However, we believe that this synonymy is premature Unlike early Eocene equids, Epihippus is a until much larger samples of each species are relatively rare component of middle Eocene faunas in available for further comparison and, based on North America. After more than 80 years of differences in size and following MacFadden (1980, collecting land mammals from Eocene strata in 1998), we recognize both species as valid. Thus, southern California by various investigators, the first based on the measurements provided by Hanson specimen of Epihippus was discovered in 1991 at (1996) for the two Epihippus specimens from the Mission del Oro by Stephan Walsh during a Hancock Quarry, we believe they should be referred paleontological mitigation program. Walsh (1996b) to E. uintensis instead of E. gracilis. The age included this specimen as Epihippus sp. in a faunal assignment of the Hancock Quarry has been debated, list of the Mission del Oro Local Fauna, but did not for example Hanson (1989, 1996) and Lander and describe or illustrate the specimen. Since 1996, Hanson (2006) regarded it as early Duchesnean in numerous paleontological mitigation programs have age, but most other investigators have regarded it as been conducted in California for the commercial latest Uintan in age (e.g., Lucas et al., 2004; development of properties, which have resulted in the Mihlbachler, 2007; Kelly et al., 2012). As noted discovery of additional specimens of Epihippus from above, if Duchesnehippus is regarded as generically three localities in the Santiago Formation. Here we distinct from Epihippus and the age assignment by provide detailed descriptions of the specimens, which Mihlbachler and Deméré (2009) for the we refer to two different species. The smaller Harpagolestes Quarry is correct, then the new record Epihippus gracilis is recorded from a new early of E. uintensis from Ocean Ranch would confirm a Uintan fauna, the Rancho Mission Viejo Local geochronologic range extension of the species into Fauna, of Orange County (Table 2). The larger E. the earliest Duchesnean. uintensis is recorded from the late Uintan or early Duchesnean? Mission del Oro Local Fauna and AKNOWLEDGMENTS locality SDSNH 4131 at Legoland, and the earliest Duchesnean Harpagolestes Quarry (SDSNH 4730) at We are thankful to the Rancho Mission Viejo Ocean Ranch in San Diego County. These are the (RMV) and, in particular, Steven Shea and Laura only specimens of Epihippus so far known from Coley Eisenburg of RMV, for their considerate California and extend the geographic range of E. support of the paleontological impact mitigation gracilis and E. uintensis to the southern part of the program that lead to the discovery of the Rancho West Coast. We also document the occurrence of a Mission Viejo Local Fauna. We are grateful to rhinocerotoid from locality SDSNH 4131, whose Thomas Deméré and Kesler Randall of the SDMNH taxonomic status is uncertain, but likely represents for providing loans of specimens for this study. either Uintaceras or Teletaceras. Special thanks are given to Mark Roeder of the Although some investigators regard SDMNH and the Archeological Resource Duchesnehippus from the middle Duchesnean of Management Corporation (ARMC), Carol Demcak, Utah and Wyoming as a junior synonym of Patrick Riseley and Hugo Lozano of the ARMC for Epihippus (e.g., MacFadden,1980; Hanson, 1996), providing geologic and locality data from the we follow Rasmussen et al. (1999b), Gunnell et al. paleontological mitigation program at Rancho (2009) and Kelly et al. (2012) and consider it a valid Mission Viejo, and Michaela Adler and Crystal genus. Epihippus gracilis has been previously Cortez of the Cooper Center, Orange County, recorded from the early to late Uintan of Utah, California, for their help in the curation of the Wyoming and Texas (Forstén, 1971; MacFadden, specimens from Rancho Mission Viejo. Dr. Richard 1980, 1998; Eaton, 1985; Westgate, 1990; Gunnell et Klein and Brent Klein of Sierra Cosmetic Dental al., 2009). Epihippus uintensis has been previously Center, Carson City, Nevada, graciously allowed recorded from the early to late Uintan of Utah, access to their radiographic equipment for analysis of KELLY AND MURPHEY—EPIHIPPUS FROM SOUTHERN CALIFORNIA 27

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